On Zr Substitution in T′-Type Nd–Ce–Cu–O System.

The effect of tetravalent Zr substitution (≤2 at%) at the Cu site in T'-type Nd[sub 2-x]Ce[sub x]CuO[sub 4-δ] (NCCO), x = 0.12, 0.14, 0.15, on the superconducting (SC) behavior is investigated. EDX analyses of the samples clearly reveal the presence of only ∼0.5 at% Zr in the T'-phase. Irrespective of the Ce content (0.12 ≤ x ≤ 0.15), T[sub c] is found to depress with Zr. A fall in T[sub c] of ∼2 K is observed due to 0.5 at% Zr[sup 4+] in x = 0.14 samples, while the NCCO (x = 0.12) on substitution of Zr (expected to dope 2 electrons per Zr[sup 4+] and induce superconductivity) remains non-SC. The reported conjecture regarding T[sub c] inducement due to the carrier addition of 0.03 (per formula unit) arising from 3 at% In[sup 3+] (or Ga[sup 3+]) substitution for Cu in Nd[sub 1.88]Ce[sub 0.12]CuO[sub 4-δ] [Ayoub et al., Physica C170, 211 (1990); Felner et al., Phys. Rev. B40, 11366 (1989)] is not applicable for the Zr-substituted NCCO. [ABSTRACT FROM AUTHOR]